As a descendant of actual Italian peasants – the photo of one black-clad great-great-grandmother, clutching a scythe, a patch covering her empty eyesocket and looking like a jovial grim reaper, is a particular family favourite – I approached Paesan with a degree of caution. Turns out there's nothing about the place that doesn't make me want to grab Nonna Fedele's scythe and put it to fruitful use.

Why does it give me such a bad dose of the pip? Is it that they've ripped off their entire look – from the reused Crodino bottles, tomato tin ice-buckets and salvaged chairs to the clipboard and butcher's paper menus – from Russell Norman's Polpo? I'm particularly needled by the "artfully" cracked exterior tiles. If only they'd copied the strength of Polpo's cocktails, too: our negronis are weaselly, over-iced disappointments. Or the insistence that they're purveying "cucina povera" (a style of cooking born of extreme Italian poverty)? Meat is rarely used in this; and, if it is, it's of the innards and extremities variety.

Using this as a hook to serve cheap ingredients, massively marked up, to droves of affluent London thirtysomethings leaves as murky a taste in my mouth as Paesan's arancini. Oh, and how does steak "tagliata" with parmesan and Roman misticanza salad sit under this banner? Answer: it doesn't. The whole thing is just so much clunky marketing coglioni.

Anyway, who cares, if the food is great, right? If only. Some of it is so actively unpleasant it defeats the pal, who's been known to eat day-old pizza with anchovies and salad cream for breakfast. The risotto, with radicchio, gorgonzola and dusty-tasting walnuts, makes me think of those medieval drawings of lions and elephants by people who'd never seen the animals. This, dense and stodgy, constructed more like a pilau and tasting viciously of raw garlic, comes across as if it's been made by someone with no experience of an actual risotto. There are orecchiette, Puglia's favourite ear-shaped pasta, with trend-ticking n'duja and cavolo nero. Well, allegedly: all we can taste is heat and smoked paprika. Perhaps the sausage and brassica have been microwave-nuked? It's as lava-hot when we give up on it as it was when we started.

Gnudi are a tricky number to pull off: featherlight ricotta dumplings, all air and fragrance. Paesan's feel as if they've been made from masticated blotting paper. Their sauce tastes freakishly like a tin of Sainsbury's chopped tomatoes with onion and basil tipped on top.

I've been waiting for pizza fritta (fried) to hit the mainstream over here: this wonderfully reprehensible carbfest was born in Naples and has become a bit of a thing in New York. When done well, as at Naples' Starita, it's the snack of the gods. Paesan's version is thick, doughy, raw-tasting, dotted with "fennel salsiccia" as compacted and dun-coloured as Findus's finest.

And those woeful arancini – lemon and courgette, they say. All we get is salt, dried-tasting herbs and a footy whiff suggestive of that parmesan that comes in cardboard drums and looks like what's left in the bottom of your Ped Egg callus remover. The consistency is soggy pap.

I look at our leftover risotto and am struck by an unnerving thought. But I'm not going there, I'm not. Is there anything good? I'll grudgingly allow them the fritto misto: the fish are fresh and it's fried well enough. But it lacks any form of seasoning. Perhaps they ran out after the arancini.

That this derivative throwback exists in the same street as Moro and Caravan smacks of sheer gall. That it's rammed to its walls demonstrates how depressingly easy it is to snow the punters. Paesan's corporate speak whiffles on about "cucina povera" being "a way of life" and talking "from one paesan to another". The owners are also responsible for the tourist trap Pasta Brown in Covent Garden.